We introduce a simple approach to segment in homogeneous phases a long-duration record of locomotion data consisting of body segment acceleration and foot pressure information only. The association of acceleration norms with impact detections allows us to successfully apply K-means algorithm in order to automatically classify the locomotion in terms of walking and various running speeds. The method is validated on experimental data. One subject, equipped with IMUs and foot pressure units is asked to successively walk and run around an indoor running track. The algorithm is able to detect the different types of motions.

This paper describes a method for providing in real time a reliable synchronization signal for cyclical motions such as steady-state walking. The approach consists in estimating online a phase variable on the basis of several implicit central pattern generator associated with a set of sensors. These sensors can be of any kind, provided their output strongly reflects the timed motion of a link. They can be, for example, spatial position or orientation sensors, or foot sole pressure sensors. The principle of the method is to use their outputs as inputs to nonlinear observers of modified Van der Pol oscillators that provide us with several independent estimations of the overall phase of the system. These estimations are then combined within a dynamical filter constituted of a Hopf oscillator. The resulting phase is a reliable indexing of the cyclic behavior of the system, which can finally be used as input to low-level controllers of a robot. Some results illustrate the efficiency of the approach, which can be used to control robots.

This paper deals with a new control approach for biped robots. The technique is inspired by the prediction capability of human being. Optimal computations over a moving horizon are performed with a set of constraints which is modified online to be adapted to the obstacle-filled environment. Simulation results show the efficiency of the algorithm in the case of a gait on flat terrain and steep stairs.

Biped robots have specific dynamical constraints and stability problems which reduce significantly their motion range. In these conditions, motion planning used for mobile robots cannot be applied to biped robots. In this paper, the path planning problem is seen as finding a sequence of footholds in a 3D environment, keeping robot stability, motion continuity and working within the structural constraints of the biped. The designed path planner contains two parts : The first one determines a reference path which maximises success rate in view of biped capabilities. This reference track is computed by the well know A* search in the graphs algorithm. The second part of the path planner is a path tracking algorithm which makes the robot follow the reference track. Simulation results concern the anthropomorphic 15 degrees of freedom robot BIP2000.

We use an alternative formulation of the Euclidean Plucker coordinates to define the new normalized Plucker coordinates for alignment of lines. This concept is more relevant than usual image alignment to position a single calibrated camera with respect to a set of known 3D lines. An explicit control law is derived which realizes such a task both for one or several lines. It is tested by positioning the camera with respect to an orthogonal trihedron. This application is all the more challenging in that it requires depth to be observed. We do this by using the image projection of a laser pointer and adequately completing the control law.

This paper describes the progress of the BIP2000 project. This project is aimed at the realization of the lower part of an anthropomorphic biped robot. The robot consists of two legs, two feet, a pelvis and a trunk. It has 15 active joints. The mass distribution, the kinematics and the capacities of the robot in terms of joint torques are close to the ones of humans. The transmissions are specific screw/nut-based systems which have good dynamic performances and small size. They are arranged in parallel at the ankles and at the trunk/pelvis linkage. The control schemes are either based on a control of the center of mass associated with suitable task functions, or take dynamically into account the unilateral constraints foot/ground. The robot has been built and tested, the computer control architecture has been realized and connected with the robot, and the basic control schemes have been implemented.

We address visual servoing through a fixed stereo rig using an image Jacobian. Existing methods are based on the stacking of monocular servo image Jacobians, resulting in largely over-constrained control commands. In this paper we formally show that the epipolar constraint between two images can be taken into account explicitly. We then show that use of stereo significantly increases the quality of the servo task execution, especially where precision, robustness and smoothness of movement is concerned.

We present a visual serving approach to the problem of object grasping and more generally, to the problem of aligning an end-effector with an object. First, we extend the method proposed by Espiau et al. (1992) to the case of a camera which is not mounted onto the robot being controlled, and we stress the importance of the real-time estimation of the image Jacobian. Next, we show how to represent a grasp or more generally, an alignment between two solids in 3D projective space using an uncalibrated stereo rig. Such a 3D projective representation is view-invariant in the sense that it can be easily mapped into an image set-point without any knowledge about the camera parameters. Finally, we perform an analysis of the performances of the visual servoing algorithm and of the grasping precision that can be expected from this type of approach.

In this paper we present a preliminary study concerning the stabilization of an underwater free-floating remotely operated vehicle fitted with a redundant manipulator. The controller structure follows the Orccad approach for robotic systems programming, which gathers control laws in continuous time at the low levels and discrete time logical aspects at higher levels. After being designed and verified, the basic actions of individual subsystems are logically composed to build more complex procedures up to a full mission design. While the system's performance can be checked using realistic simulations, crucial properties such as deadlock avoidance, safety and liveness are formally verified at both levels, using in particular some advantages of synchronous programming and associated tools. The approach is illustrated through simulation results while experiments are in progress.

This paper proposes an analysis of the behavior of perhaps the simplest biped robot: the compass gait model. It has been shown previously that such a robot can walk down a slope indefinitely without any actuation. Passive motions of this nature are of particular interest since they may lead us to strategies for controlling active walking machines as well as to a better understanding of human locomotion. We show here that, depending on the parameters of the system, passive compass gait may exhibit 1-periodic, 2/sup n/-periodic and chaotic gaits proceeding from cascades of period-doubling bifurcations. Since compass equations are quite involved (they combine nonlinear differential and algebraic equations in a 4-dimensional space), our investigations rely, in part, on numerical simulations.

It is well-known that a suitably designed unpowered mechanical biped robot can "walk" down an inclined plane with a steady gait. The characteristics of the gait (e.g., velocity, time period, step length) depend on the geometry and the inertial properties of the robot and the slope of the plane. A passive motion has the distinction of being "natural" and is likely to enjoy energy optimality. Investigation of such motions may potentially lead us to strategies useful for controlling active walking machines. In this paper we demonstrate that the nonlinear dynamics of a simple passive "compass gait" biped robot can exhibit periodic and stable limit cycle. Kinematically the robot is identical to a double pendulum (or its variations such as the Acrobot and the Pendubot). Simulation results also reveal the existence of a stable gait with unequal step lengths. We also present an active control scheme which enlarges the basin of attraction of the passive limit cycle.

For underwater vehicles to be self-sufficient in an a priori unknown environment, feedback from the environment through altitude sensors is essential. This paper presents how this feedback can be efficiently achieved for AUVs in which different simultaneous tasks have to concur to the achievement of a mission. The approach is based on the task-function approach, with a continuous switching between the involved tasks. The presented application concerns the use of acoustic range/altitude sensors in the control of a fully-actuated AUV.

A robotic application is defined by a set of scheduled actions, each action being modeled as a robot-task with functional and behavioral aspects. The authors propose a programming approach located at an intermediary level between objective and object levels, called the task-level. The basic feature consists of using a synchronous language (Esterel) as the target language of an application programming language that is able to express in a natural way the logical and temporal dependencies of the actions. The synchrony assumption induces the need for the design of a synchronous/asynchronous interface to be associated with the computer system. This aspect is considered. The proposed language is presented, and an example of a robotic application is given.>

The authors present some design issues for a task-level controller based on a specific control approach. The achievement of a robotic application requires the use of a large set of cooperating devices such as manipulators and sensors. An application is performed by scheduling several actions of the system. Each action is modeled with a functional aspect (control law) and a behavioral one (reactions on events). These two aspects are combined in a single object, the robot-task. An object-oriented approach was used to model these actions. The synchronous language Esterel was used both to program an application at the end-user level and to program the behavioral part of the robot-tasks at the control level. The main design issues of a real-time controller able to implement and perform these actions are outlined.>

Vision-based control in robotics based on considering a vision system as a specific sensor dedicated to a task and included in a control servo loop is described. Once the necessary modeling stage is performed, the framework becomes one of automatic control, and stability and robustness questions arise. State-of-the-art visual servoing is reviewed, and the basic concepts for modeling the concerned interactions are given. The interaction screw is thus defined in a general way, and the application to images follows. Starting from the concept of task function, the general framework of the control is described, and stability results are recalled. The concept of the hybrid task is presented and then applied to visual sensors. Simulation and experimental results are presented, and guidelines for future work are drawn in the conclusion.>

An application is described of the so-called visual servoing approach to robot positioning with respect to an object and to target tracking. After briefly discussing how the task function approach can be applied to tasks which include the use of visual features, the authors give a simplified control expression which explicitly takes into account the case of moving objects. Estimating the target velocity while performing the tracking control leads to a kind of adaptive control scheme. The authors then consider the specific case of a square target and derive all the components of the control scheme. They present some experimental results obtained at the video rate in an experimental system composed of a camera mounted on the end effector of a six-DOF robot.>

This paper presents a scheme allowing to estimate parameters which describe geometrical structures in a 3D scene by only using informations issued from a sequence of images provided by a mobile vision sensor with known motion. We first recall the basic used models : points and lines, and then relate their perspective projection in the image plane to the camera motion. Some techniques of recursive filtering are used into the sequence of images to incrementaly build the 3D scene all along the displacement of the camera. Some experimental results in the field of robotics are given.

The paper gives an overview of the different aspects of Nuclear services (Intervention, Decomissioning, Maintenance). A presentation of today and future needs in these fields for Teleoperation with sensor based controls is reviewed. The present achievements of French efforts in CAT (computer assisted Teleoperation) applied to bilateral force feedback Telemanipulators is derived.